关于mybatis缓存于一级缓存

对于mybatis框架。仿佛工作中一直是在copy着使用。对于mybatis缓存。并没有一个准确的认知。趁着假期。学习下mybatis的缓存。这篇主要学习mybatis的一级缓存。

为什么使用缓存

其实，大家工作久了，就知道很多瓶颈就是在数据库上。

初识mybatis一级缓存
当然我们还是通过代码来认识下mybatis的一级缓存

代码演示
详细代码见github，这里只展示重要的代码片段

tempMapper.xml

select * from temp where id = #{id}

TempTest
public class TempTest {

Logger logger = Logger.getLogger(this.getClass());
@Test
public  void test() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = build.openSession();
TempEntity tempEntity1 = sqlSession.selectOne("dao.TempDao.getById", 1);
logger.info(tempEntity1);
TempEntity tempEntity2 = sqlSession.selectOne("dao.TempDao.getById", 1);
logger.info(tempEntity2);
logger.info(tempEntity1 == tempEntity2);
}

}
3.运行结果

2020-06-26 08:57:37,453 DEBUG [dao.TempDao.getById] - ==> Preparing: select * from temp where id = ?
2020-06-26 08:57:37,513 DEBUG [dao.TempDao.getById] - > Parameters: 1(Integer)
2020-06-26 08:57:37,538 DEBUG [dao.TempDao.getById] - < Total: 1
2020-06-26 08:57:37,538 INFO [TempTest] - TempEntity{id=1, value1=‘11111’, value2=‘aaaaa’}
2020-06-26 08:57:37,538 INFO [TempTest] - TempEntity{id=1, value1=‘11111’, value2=‘aaaaa’}
2020-06-26 08:57:37,538 INFO [TempTest] - true
总结
http://v.qq.com/x/search/?q=%E8%80%81%E8%A1%97%E5%8D%8E%E7%BA%B3%E5%BC%80%E6%88%B7_18183615678

4.1 从上面的结果，我们可以看到,第二次查询的时候，就直接没有查询数据库，并且返回的是同一个对象。证明第二次走的就是缓存。
4.2 一级缓存是默认开启的。我们并没有在代码中配置任何关于缓存的配置
4.3 代码回顾

mybatis一级缓存命中原则
mybatis是怎么样判断某两次查询是完全相同的查询？

1.statementId
1.1 mapper.xml

<select id="getById1" resultType="entity.TempEntity">
select * from  temp where id = #{id}
</select>

<select id="getById2" resultType="entity.TempEntity">
select * from  temp where id = #{id}
</select>

1.2 test

@Test
public  void test() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = build.openSession();
TempEntity tempEntity1 = sqlSession.selectOne("dao.Temp2Dao.getById1", 1);
logger.info(tempEntity1);
TempEntity tempEntity2 = sqlSession.selectOne("dao.Temp2Dao.getById2", 1);
logger.info(tempEntity2);
logger.info(tempEntity1 == tempEntity2);
}

1.3 结果

2020-06-26 09:19:09,926 DEBUG [dao.Temp2Dao.getById1] - ==> Preparing: select * from temp where id = ?
2020-06-26 09:19:09,957 DEBUG [dao.Temp2Dao.getById1] - > Parameters: 1(Integer)
2020-06-26 09:19:09,969 DEBUG [dao.Temp2Dao.getById1] - < Total: 1
2020-06-26 09:19:09,969 INFO [TempTest] - TempEntity{id=1, value1=‘11111’, value2=‘aaaaa’}
2020-06-26 09:19:09,969 DEBUG [dao.Temp2Dao.getById2] - ==> Preparing: select * from temp where id = ?
2020-06-26 09:19:09,970 DEBUG [dao.Temp2Dao.getById2] - > Parameters: 1(Integer)
2020-06-26 09:19:09,970 DEBUG [dao.Temp2Dao.getById2] - < Total: 1
2020-06-26 09:19:09,971 INFO [TempTest] - TempEntity{id=1, value1=‘11111’, value2=‘aaaaa’}
1.4 总结
要求查询的statementId必须完全相同，否则无法命中缓存，即时两个查询语句、参数完全相同

2.查询参数
我们用不同的参数查询，一个传1 一个传2
2.1 test

@Test
public  void testParam() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = build.openSession();
TempEntity tempEntity1 = sqlSession.selectOne("dao.Temp2Dao.getById1", 1);
logger.info(tempEntity1);
TempEntity tempEntity2 = sqlSession.selectOne("dao.Temp2Dao.getById1", 2);
logger.info(tempEntity2);
logger.info(tempEntity1 == tempEntity2);
}

2.2 结果

2020-06-26 09:24:33,107 DEBUG [dao.Temp2Dao.getById1] - ==> Preparing: select * from temp where id = ?
2020-06-26 09:24:33,148 DEBUG [dao.Temp2Dao.getById1] - > Parameters: 1(Integer)
2020-06-26 09:24:33,162 DEBUG [dao.Temp2Dao.getById1] - < Total: 1
2020-06-26 09:24:33,162 INFO [TempTest] - TempEntity{id=1, value1=‘11111’, value2=‘aaaaa’}
2020-06-26 09:24:33,162 DEBUG [dao.Temp2Dao.getById1] - ==> Preparing: select * from temp where id = ?
2020-06-26 09:24:33,163 DEBUG [dao.Temp2Dao.getById1] - > Parameters: 2(Integer)
2020-06-26 09:24:33,164 DEBUG [dao.Temp2Dao.getById1] - < Total: 1
2020-06-26 09:24:33,164 INFO [TempTest] - TempEntity{id=2, value1=‘22222’, value2=‘bbbb’}
2020-06-26 09:24:33,164 INFO [TempTest] - false

2.3 总结

要求传递给sql的传递参数相同，否则不会命中缓存

3.分页参数
3.1 传不同的分页参数

@Test
public  void testPage() throws IOException {
InputStream inputStream = Resources.getResourceAsStream("mybatis.xml");
SqlSessionFactory build = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = build.openSession();
RowBounds rowBounds1 = new RowBounds(0,1);
List<TempEntity> tempEntity1 = sqlSession.selectList("dao.Temp2Dao.getList", null,rowBounds1);
logger.info(tempEntity1);
RowBounds rowBounds2 = new RowBounds(0,2);
List<TempEntity> tempEntity2 = sqlSession.selectList("dao.Temp2Dao.getList",null, rowBounds2);
logger.info(tempEntity2);
logger.info(tempEntity1 == tempEntity2);
}

3.2 结果

2020-06-26 10:10:33,060 DEBUG [dao.Temp2Dao.getList] - ==> Preparing: select * from temp where 1=1
2020-06-26 10:10:33,101 DEBUG [dao.Temp2Dao.getList] - ==> Parameters:
2020-06-26 10:10:33,116 INFO [TempTest] - [TempEntity{id=1, value1=‘11111’, value2=‘aaaaa’}]
2020-06-26 10:10:33,116 DEBUG [dao.Temp2Dao.getList] - ==> Preparing: select * from temp where 1=1
2020-06-26 10:10:33,116 DEBUG [dao.Temp2Dao.getList] - ==> Parameters:
2020-06-26 10:10:33,118 INFO [TempTest] - [TempEntity{id=1, value1=‘11111’, value2=‘aaaaa’}, TempEntity{id=2, value1=‘22222’, value2=‘bbbb’}]
2020-06-26 10:10:33,118 INFO [TempTest] - false
3.3 总结

要求分页参数必须相同，否则无法命中缓存。缓存的粒度是整个分页查询结果，而不是结果中的每个对象

1. sql语句
   4.1 mapper文件

   select * from temp id = #{id} 1=1 and id = #{id}

这个就不测试了。
4.2 总结
要求传递给jdbc的sql 必须完全相同。就算是1=1 不起作用 也不行

5.环境
这里的环境指的的是 和 也是会影响的
http://v.qq.com/x/search/?q=%E5%8D%8E%E7%BA%B3%E5%85%AC%E5%8F%B8%E5%BC%80%E6%88%B7_18183615678
http://v.qq.com/x/search/?q=%E5%8D%8E%E7%BA%B3%E7%82%B9%E5%87%BB%E5%BC%80%E6%88%B7_18183615678
























总结